SPLIT_EDGE_3D inserts a vertex at a specified point on a selected
edge.
----(SPLIT_EDGE_3D)----|SELECT S_EDGE_3D|---|point 3D|---->
This action has no options.
Use this action to insert a vertex at a chosen point along an
edge.
SPLIT_EDGE_3D : "pick edge" "pick point"
SPLIT terminate action